Image sensing apparatus with electronic shutter function and mechanical shutter function, and image sensing method

ABSTRACT

An image sensing apparatus having an electronic shutter for controlling the charge accumulation time of an image sensing element and a mechanical shutter for releasing/shielding an optical path to the image sensing element includes an electronic shutter mode of controlling the image sensing time mainly by the electronic shutter and a mechanical shutter mode of controlling the image sensing time mainly by the mechanical shutter. In the electronic shutter mode, the operations of the electronic and mechanical shutters are controlled to overlap each other, and a charge reading period of the image sensing element and part of a release operation period of the mechanical shutter are controlled to overlap each other.

This application is a continuation of prior application Ser. No.11/109,641, filed Dec. 5, 2001, which claims priority under 35 U.S.C.§120. This application claims a benefit of priority based on JapanesePatent Application No. 2000-371959, filed on Dec. 6, 2000, which ishereby incorporated by reference herein in its entirety as if fully setforth herein.

FIELD OF THE INVENTION

The present invention relates to an image sensing method and imagesensing apparatus and, more particularly, to an image sensing apparatuswith an electronic shutter function and mechanical shutter function andan image sensing method.

BACKGROUND OF THE INVENTION

An electronic camera for capturing an image by using an image sensingelement such as a CCD (Charge-Coupled Device) for converting lightincoming through a photographing lens has an electronic shutter functionof controlling the image sensing time by controlling the imaging sensingoperation time for receiving light which forms an image. Usually, theelectronic camera also has a mechanical shutter for reducing smear orthe like caused by redundant light after the image sensing element hasreceived a necessary quantity of light. Further, the electronic cameraperforms slit exposure using a focal plane shutter, like exposure of ageneral silver halide film.

As this electronic camera, an electronic camera disclosed in JapanesePatent Laid-Open No. 11-212136 (to be referred to as the first prior arthereinafter) uses a mechanical shutter to control exposure in normalnatural light photography, and uses an electronic shutter to controlexposure in high-speed photography using an electronic flash device.

As the above-mentioned electronic camera, the following electroniccamera is disclosed in Japanese Patent Laid-Open No. 11-234574 (to bereferred to as the second prior art hereinafter). When exposure iscontrolled by mechanical and electronic shutters, the driving starttiming of the mechanical shutter or the charge accumulation start timingof the electronic shutter is adjusted to adjust an individual variationerror caused by a mechanical delay until actual operation of themechanical shutter starts in response to an electrical driving startsignal for designating a shutter operation in the mechanical shuttersince the electrical driving start signal is issued.

In the first prior art, however, the mechanical shutter controlsexposure in normal natural light photography, and the highest speed of ashutter speed generally adopted in the electronic camera depends on theperformance of the mechanical shutter. Achievement of a high speed of,e.g., 1/8,000 sec requires a high-performance mechanical shutter. Theshutter itself becomes a complicated mechanism, resulting in a largeshutter and high cost. The mechanical shutter is technically difficultto drive at a high speed (e.g., 1/16,000 sec or more).

In the first prior art, the mechanical shutter is generally driven bystarting driving of a front blade in response to a front blade drivingstart signal after the end of a photographing sequence for a precedingframe. The end of driving the front blade is detected by a switch fordetecting the end of driving the front blade. Charges are accumulated bya CCD or the like. After charge accumulation ends, driving of a rearblade starts in response to a rear blade driving start signal. The endof driving the rear blade is detected by a switch for detecting the endof driving the rear blade. Then, normal read of signal charges isperformed. This arrangement warrants reliable exposure control. However,since the next operation starts upon the end of each operation, the timetaken for a photographing sequence per frame is prolonged. Since thenext operation starts after the operation status of each switch ismonitored, the time taken for a photographing sequence is prolonged.This disables high-speed sequential shooting of an electronic camera.

In the second prior art, variations in exposure control time caused bythe mechanical delay between the mechanical shutters of respectiveelectronic cameras are corrected by adjusting the application timing ofa mechanical shutter driving pulse or the charge accumulation starttiming of the electronic shutter. This adjustment is done for eachelectronic camera, which increases the time taken to assemble and adjustthe electronic camera, and increases the cost. This electronic camerarequires a jig for measuring and adjusting variations in exposure timecaused by the mechanical delay of the mechanical shutter. If the chargeaccumulation start timing of the electronic shutter is adjusted, therelease time lag of the electronic camera varies between respectiveelectronic cameras. This is inconvenient for a user who uses a pluralityof electronic cameras because photographs taken by releasing theshutters of the electronic cameras become different.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its first object to provide an image sensingmethod and image sensing apparatus capable of preventing degradation ofan image caused by smear of an image sensing element.

It is the second object of the present invention to provide an imagesensing method and image sensing apparatus capable of preventing theuser from feeling incompatibility in switching a photographing sequence.

It is the third object of the present invention to provide an imagesensing method and image sensing apparatus capable of achieving a stableframe speed in sequential shooting and an increase in speed withoutmeasuring and adjusting variations in exposure time caused by themechanical delay of a mechanical shutter.

According to the present invention, the foregoing object is attained byproviding an image sensing method of sensing an image by an imagesensing apparatus having an electronic shutter for controlling a chargeaccumulation time of an image sensing element and a mechanical shutterfor releasing/shielding an optical path to the image sensing element,the method having a first control mode of controlling an image sensingperiod mainly by the electronic shutter, comprising: a control step ofcontrolling operations of the electronic and mechanical shutters so asto overlap each other, and a charge reading period of the image sensingelement and part of a release operation period of the mechanical shutterare controlled to overlap each other.

According to the present invention, the foregoing object is alsoattained by providing an image sensing apparatus having an electronicshutter for controlling a charge accumulation time of an image sensingelement and a mechanical shutter for releasing/shielding an optical pathto the image sensing element, and having a first control mode ofcontrolling an image sensing time mainly by the electronic shutter,comprising: a controller adapted to control operations of the electronicand mechanical shutters so as to overlap each other, and controlling acharge reading period of the image sensing element and part of a releaseoperation period of the mechanical shutter to overlap each other.

Further, the foregoing object is also attained by providing an imagesensing method of sensing an image by an image sensing apparatus havingan electronic shutter for controlling a charge accumulation time of animage sensing element and a mechanical shutter for releasing/shieldingan optical path to the image sensing element, the method having acontrol mode of controlling an image sensing time mainly by themechanical shutter, comprising: a control step of draining unwantedcharges of transfer means prior to transfer of charges of the imagesensing element in the control mode.

Furthermore, the foregoing object is also attained by providing an imagesensing apparatus having an electronic shutter for controlling a chargeaccumulation time of an image sensing element and a mechanical shutterfor releasing/shielding an incident optical path to the image sensingelement, and having a control mode of controlling an image sensing timemainly by the mechanical shutter, comprising: a controller adapted todrain unwanted charges of transfer means for transferring charges of theimage sensing element, prior to transfer of charges of the image sensingelement in the control mode.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate an embodiment of the inventionand, together with the description, serve to explain the principles ofthe invention.

FIG. 1 is a sectional side view showing a structure of an electroniccamera as an image sensing apparatus according to an embodiment of thepresent invention;

FIG. 2 is a block diagram showing an internal arrangement of theelectronic camera as the image sensing apparatus according to theembodiment of the present invention;

FIG. 3 is a timing chart showing a sequence in the mechanical shuttercontrol mode of the electronic camera as the image sensing apparatusaccording to the embodiment of the present invention;

FIG. 4 is a timing chart showing a sequence in the electronic shuttercontrol mode of the electronic camera as the image sensing apparatusaccording to the embodiment of the present invention;

FIG. 5 is a timing chart showing the control sequence of a mechanicalshutter in the electronic shutter control mode of FIG. 4;

FIG. 6 is a view showing the shutter speed control regions of theelectronic and mechanical shutter control modes in the electronic cameraas the image sensing apparatus according to the embodiment of thepresent invention;

FIG. 7 is a flow chart showing the operation flow of the electroniccamera as the image sensing apparatus according to the embodiment of thepresent invention; and

FIG. 8 is a flow chart showing the operation flow of the electroniccamera as the image sensing apparatus according to the embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described indetail in accordance with the accompanying drawings.

FIG. 1 is a sectional side view showing the structure of an electroniccamera as an image sensing apparatus according to the embodiment. InFIG. 1, reference numeral 1 denotes an electronic camera main body; and2, a photographing lens for forming an object image on an imaging plane.The photographing lens 2 is detachably attached to the electronic cameramain body 1. The photographing lens 2 has an imaging lens 3 for formingan object image on an imaging plane, and a lens driving device 4 fordriving the imaging lens 3. Further, the photographing lens 2 includesaperture blades 5 for controlling exposure, and an aperture drivingdevice 6 for driving the aperture blades 5.

The imaging lens 3 is simplified in FIG. 1, but is formed from one or aplurality of lenses. The imaging lens 3 may be a single-focal-length(fixed-focus) lens or a variable-focal-length lens such as a zoom lensor step zoom lens.

In FIG. 1, reference numeral 7 denotes a main mirror for guiding lightfrom an object (referred to as object image hereinafter) formed by thephotographing lens 2 to a focusing screen 8 (to be described later), andtransmitting part of the object image to guide it to a focus detectiondevice 13 (to be described later) via a sub-mirror 12 (to be describedlater). The main mirror 7 is alternatively, freely moved by a mirrordriving device (not shown) to a position where the main mirror 7 allowsobserving an object image via a viewfinder and a retract position wherethe main mirror 7 is retracted from the optical path of the object imagein photographing.

The object image which is guided by the photographing lens 2 andreflected by the main mirror 7 is formed on the focusing screen 8. Inviewfinder observation, an object image is formed on the focusing screen8. Reference numeral 9 denotes an optical member for reflecting anobject image formed on the focusing screen 8 into an erect image. Theoptical member 9 is a pentaprism in this embodiment. Reference numeral10 denotes an eyepiece lens device for guiding, to the photographer'seye, the object image which has been reflected into an erect image bythe optical member 9.

Reference numeral 11 denotes a photometry device for measuring via theoptical member 9 the brightness of an object image formed on thefocusing screen 8 in viewfinder observation. The electronic camera 1according to this embodiment controls exposure on the basis of an outputsignal from the photometry device 11.

The sub-mirror 12 reflects the object image having passed through a partof the main mirror 7, and guides the object image to the focus detectiondevice 13 (to be described later) arranged below a mirror box (notshown). The sub-mirror 12 is coupled with the main mirror 7 or themirror driving device (not shown) for driving the main mirror 7. Thesub-mirror 12 is freely moved to a retract position where the sub-mirror12 is retracted from the optical path of an object image inphotographing and otherwise to a position where the sub-mirror 12 guidesan object image having passed through the main mirror 7 to the focusdetection device 13.

The lens driving device 4 of the photographing lens 2 is controlled onthe basis of an output signal from the focus detection device 13. Thefocus is adjusted by the imaging lens 3. Reference numeral 14 denotes amechanical shutter for mechanically controlling a period during which anobject image is incident on the imaging plane. The mechanical shutter 14is a focal plane shutter having front blades 14 a which shield an objectimage in viewfinder observation, and are retracted from the optical pathof the object image to start exposure in accordance with a releasesignal in photographing, and rear blades 14 b which are retracted fromthe optical path of an object image in viewfinder observation, andshield the object image at a predetermined timing after the start oftraveling (driving) the front blades 14 a in photographing.

Reference numeral 15 denotes a solid-state image sensing element forsensing an object image formed by the photographing lens 2 andconverting it into an electrical signal. As the solid-state imagesensing element 15, a known two-dimensional image sensing device isused. The image sensing device includes devices of various types such asa CCD type, MOS type, CID type, and any type of image sensing device canbe adopted. This embodiment employs an interline CCD (Charge-CoupledDevice) type image sensing element which is constituted bytwo-dimensionally arranging photoelectric conversion elements(photosensors) and outputs signal charges accumulated in eachphotosensor via vertical and horizontal transfer paths. The solid-stateimage sensing element 15 has a so-called electronic shutter function ofcontrolling the accumulation time of charges accumulated in eachphotosensor (shutter speed). Reference numeral 16 denotes an electricalboard which is electrically, mechanically coupled to the solid-stateimage sensing element 15 and holds it.

FIG. 2 is a block diagram showing the internal arrangement of theelectronic camera according to the embodiment.

In FIG. 2, the same reference numerals as in FIG. 1 denote the sameparts. In FIG. 2, the electronic camera is mainly constituted by thelens driving device 4 for driving the photographing lens 2, themechanical shutter 14, the solid-state image sensing element 15, ananalog signal processing circuit 20, an A/D converter 22, a main signalprocessing circuit 24, a memory 26, a D/A converter 28, an externaldisplay device 30, a compression/decompression circuit 32, a memory card34, a control circuit 36, and a CPU (Central Processing Unit) 38.

An object image having passed through the photographing lens 2 isrestricted in light quantity by the aperture blades 5 and mechanicalshutter 14, and imaged on the solid-state image sensing element 15. Atthis time, the charge accumulation time of the solid-state image sensingelement 15 is controlled via the control circuit 36. The object imageformed on the light-receiving surface of the solid-state image sensingelement 15 is converted by photosensors into signal charges of an amountcorresponding to the incident light quantity. The signal charges aresequentially read out as image sensing signals, which are supplied tothe analog signal processing circuit 20.

The analog signal processing circuit 20 includes a CDS clamp circuit andgain adjustment circuit. The analog signal processing circuit 20properly processes each image sensing signal (analog electrical signal)input from the solid-state image sensing element 15 under the control ofthe control circuit 36. The image sensing signal output from the analogsignal processing circuit 20 is converted into a digital signal by theA/D converter 22. This digital signal is output to the main signalprocessing circuit 24.

The main signal processing circuit 24 is made up of a gain adjustmentcircuit 40, offset circuit 42, histogram generation circuit 46, anddigital signal processing circuit 48. Image data output from the A/Dconverter 22 is output to the histogram generation circuit 46 anddigital signal processing circuit 48 via the gain adjustment circuit 40and offset circuit 42.

From data of one frame sent from the A/D converter 22, the histogramgeneration circuit 46 creates a histogram representing the distributionof the integral value of an image sensing signal to the signal level. Again value and offset value are determined based on the histogramcalculation. The CPU 38 controls the gain of the gain adjustment circuitand the offset value of the offset circuit via the control circuit 36.

A signal whose gain and offset have been adjusted is sent to the digitalsignal processing circuit 48. The digital signal processing circuit 48includes a luminance (Y) signal generation circuit and color difference(C) signal generation circuit. The digital signal processing circuit 48executes Y/C signal processing for a signal input from the offsetcircuit 42. The image signal having undergone Y/C signal processing bythe digital signal processing circuit 48 is temporarily stored in thememory 26.

The image data stored in the memory 26 is decoded, and then convertedinto an analog signal by the D/A converter 28. The analog signal issupplied to the external display device 30 such as a liquid crystalmonitor. The external display device 30 displays the image captured bythe solid-state image sensing element 15. The external display device 30displays a still image photographed in response to a photographing startsignal issued by the press of a shutter button (not shown).

The signal converted into an analog signal by the D/A converter 28 canbe extracted as an external image output 50 from a video output terminalor the like.

Image data obtained by photographing in response to input of aphotographing start signal is supplied from the memory 26 to thecompression/decompression circuit 32 where the data is compressed in apredetermined format (e.g., JPEG). The compressed data is recorded on arecording medium such as the memory card 34.

The recording medium can take various forms such as a smart medium andIC card. The image data recorded on the memory card 34 can be read underthe control of the CPU 38. The read image data is decompressed by thecompression/decompression circuit 32. The decompressed data is output tothe external display device 30 via the memory 26 and D/A converter 28,or supplied to a video signal output terminal (not shown) or the like soas to be output to another external device.

The CPU 38 is connected to the photometry device 11, focus detectiondevice 13, control circuit 36, histogram generation circuit 46, digitalsignal processing circuit 48, memory 26, memory card 34, and so on. TheCPU 38 conducts various calculation operations for, e.g., the exposurevalue and the focal position of the photographing lens 2 in accordancewith a predetermined algorithm. The CPU 38 systematically executes autoexposure control, auto focus control, auto flash control, auto whitebalance control, and the like. The CPU 38 controls circuits on the basisof various signals input from operation units (not shown) such as arelease button and mode setting means.

An output signal from the photometry device 11 is sent to the CPU 38,which calculates an exposure control value representing an exposuretime. The obtained exposure control value is output from the CPU 38 tothe control circuit 36. Auto exposure control, auto flash control, autowhite balance control, and the like are executed via the control circuit36.

Exposure control of the electronic camera according to this embodimentis performed in two exposure control modes: an electronic shuttercontrol mode and mechanical shutter control mode. The electronic andmechanical shutter control modes are automatically switched by thecontrol circuit 36 and CPU 38.

More specifically, the control circuit 36 controls the driving circuitof the solid-state image sensing element 15 on the basis of an exposurecontrol value sent from the CPU 38. In the electronic shutter controlmode, the charge accumulation time of the solid-state image sensingelement 15 is controlled. In the mechanical shutter control mode, theopening/closing timing of the mechanical shutter 14 is controlled, andduring exposure, the aperture driving device 6 is controlled.

FIGS. 3 to 5 are timing charts for explaining the photographingsequences of the electronic camera in the electronic and mechanicalshutter control modes. FIG. 3 shows a photographing sequence in themechanical shutter control mode, FIG. 4 shows a photographing sequencein the electronic shutter control mode, and FIG. 5 shows the controlsequence of the mechanical shutter 14 in the electronic shutter controlmode of FIG. 4.

The photographing sequence in the mechanical shutter control mode willbe explained with reference to FIG. 3. In FIG. 3, if the CPU 38determines to perform exposure control in the mechanical shutter controlmode, the control circuit 36 starts driving the front blades 14 a (i.e.,opens the closed front blades 14 a) by outputting a front bladetraveling start signal to the mechanical shutter 14 on the basis of anexposure control value from the CPU 38. At the same time, the controlcircuit 36 starts a charge accumulation operation by operating thesolid-state image sensing element 15. The control circuit 36 startsdriving the rear blades 14 b (i.e., closes the opened rear blades 14 b)by outputting a rear blade traveling start signal to the mechanicalshutter 14 on the basis of a Tv value (target image sensing time) set inaccordance with the exposure control value from the CPU 38. In thismanner, the front and rear blades 14 a and 14 b are respectively openedand closed to control exposure of the solid-state image sensing element15.

After driving of the rear blades 14 b of the mechanical shutter 14 ends,the solid-state image sensing element 15 continues the chargeaccumulation operation. To eliminate the influence of smear caused by anexcessive quantity of incident light in exposure, the solid-state imagesensing element 15 reads out and drains a smear component leaking to avertical transfer CCD before shifting signal charges accumulated inphotoelectric conversion elements to the vertical transfer CCD. Then,the solid-state image sensing element 15 ends the charge accumulationoperation, and transfers signal charges accumulated in the photoelectricconversion elements to the vertical transfer CCD. The solid-state imagesensing element 15 performs normal read which is a signal charge readoperation, and ends the photographing sequence of one frame.

The photographing sequence in the electronic shutter control mode willbe explained with reference to FIG. 4. In FIG. 4, if the CPU 38determines to perform exposure control in the electronic shutter controlmode, the control circuit 36 starts driving the front blades 14 a (i.e.,opens the front blades 14 a) by outputting a front blade traveling startsignal to the mechanical shutter 14 on the basis of an exposure controlvalue from the CPU 38. After the front blades 14 a are completelyopened, the control circuit 36 starts a charge accumulation operation byoperating the solid-state image sensing element 15, and controls thecharge accumulation time by a Tv value set based on the exposure controlvalue from the CPU 38.

The control circuit 36 starts driving the rear blades 14 b (i.e., closesthe rear blades 14 b) by outputting a rear blade traveling start signalto the mechanical shutter 14 in consideration of the charge accumulationend timing to shield light from the solid-state image sensing element15. The solid-state image sensing element 15 transfers signal chargesaccumulated in the photoelectric conversion elements at the end of thecharge accumulation time. At the driving end timing of the rear blades14 b, the solid-state image sensing element 15 performs a normal readingoperation which is a signal charge read operation, and ends thephotographing sequence of one frame.

The control sequence of the mechanical shutter 14 in the electronicshutter control mode will be described with reference to FIG. 5. In FIG.5, a front blade time lag Ti is a time until the main body aperture unit(to be referred to as an aperture hereinafter) is actually opened afterthe front blades 14 a of the mechanical shutter 14 are driven by a frontblade traveling start signal from the control circuit 36 at the start ofan exposure operation. A front blade curtain traveling time V1 is a timetaken to travel the aperture by the front blades 14 a. A rear blade timelag T2 is a time until the aperture is actually shielded from lightafter the rear blades 14 b of the mechanical shutter 14 are driven by arear blade traveling start signal from the control circuit 36 at the endof the exposure operation. A rear blade curtain traveling time V2 is atime taken to travel the aperture by the rear blades 14 b. The frontblade time lag T1, front blade curtain traveling time V1, rear bladetime lag T2, and rear blade curtain traveling time V2 vary betweenindividual cameras with a time width within a certain range owing to amechanical factor. As for variations in time lag and traveling time,subscripts “min” and “max” are attached to the shortest and longestones, respectively.

The mechanical shutter 14 is driven such that driving of the frontblades 14 a starts by a front blade traveling start signal after the endof the photographing sequence of a preceding frame (end of a normalreading operation), the end of driving of the front blades 14 a isdetected by, e.g., a switch for detecting the end of driving of thefront blades 14 a, and then a normal reading operation of signal chargesis done. This achieves reliable exposure control.

However, starting the next operation after the end of each operationprolongs a time taken for a photographing sequence per frame. Startingthe next operation after monitoring the operation status of each switchalso prolongs the time taken for the sequence, failing in high-speedsequential shooting of the electronic camera.

To prevent this, the electronic camera according to the embodimentmanages all operation start timings by the time in the electronicshutter control mode, and overlap-controls operations.

In FIG. 5, the control circuit 36 outputs a front blade traveling startsignal a time T1min before the end of a normal reading operation of apreceding frame. In this way, the control circuit 36 makes the normalreading operation of the preceding frame overlap driving of the frontblades 14 a of the mechanical shutter 14 for the next frame by the timeT1min. Charge accumulation of the next frame starts T1max+V1max afterthe output of the front blade traveling start signal.

The time between the end of the normal reading operation of thepreceding frame and the start of charge accumulation of the next frameis V1max+(T1max−T1min), which is determined by the longest time of thefront blade curtain traveling time V1 and the variation of thefrontblade time lag T1.

The control circuit 36 outputs a rear blade traveling start signal atime T2min before the end of signal accumulation of the photographingframe. In this way, the control circuit 36 makes charge accumulation ofthe photographing frame overlap driving of the rear blades 14 b of themechanical shutter 14 by the time T2min. The normal reading operation ofthe photographing frame starts T2max+V2max after the output of the rearblade traveling start signal.

The time between the end of charge accumulation of the photographingframe and the start of a normal reading operation is V2max+(T2max−T2min), which is determined by the longest time of the rear blade curtaintraveling time V2 and the variation of the rear blade time lag T2.

In exposure control using the electronic shutter control mode, theelectronic camera according to the embodiment can perform overlapcontrol of driving of the front blades 14 a of the mechanical shutter 14for a photographing frame and a normal reading operation of thepreceding frame, thereby shortening the time between the end of thenormal reading operation of the preceding frame and a chargeaccumulation operation of the photographing frame. Further, theelectronic camera can perform overlap control of a charge accumulationoperation of the photographing frame and driving of the rear blades 14 bof the mechanical shutter 14, thereby shortening the time between theend of charge accumulation of the photographing time and the start of anormal reading operation.

Not only a high-performance mechanical shutter device (having highcurtain speed) coping with high shutter speed, but also a mechanicalshutter device which exhibits a short variation in the front/rear bladetime lag can shorten the time between the end of a normal readingoperation of a preceding frame and the start of charge accumulation timeof the next frame and the time between the end of charge accumulation ofthe photographing frame and the start of a normal reading operation.Accordingly, a time required for one photographing sequence can beshortened, realizing high-speed sequential shooting.

In the electronic camera according to the embodiment, the operationsequences of the mechanical shutter 14 and solid-state image sensingelement 15 are different between the electronic and mechanical shuttercontrol modes, as shown in FIGS. 3 and 4. Thus, a time required for onesequence differs. In particular, the mechanical shutter control mode ofFIG. 3 executes vertical transfer before a normal reading operation.This prolongs the time required for one sequence in comparison with theelectronic shutter control mode of FIG. 4, which is disadvantageous tohigh-speed sequential shooting.

To avoid this, the CPU 38 of the electronic camera according to theembodiment switches the control sequence depending on the shutter speedin exposure control in consideration of the merits of respective controlsequences.

In the electronic shutter control mode, the time required for onesequence is short, and only the charge accumulation time of thesolid-state image sensing element 15 is controlled for exposure.Therefore, this mode is executed when high-shutter-speed control isrequired since very-high-shutter-speed control is possible in this mode.Low-shutter-speed control is performed in the mechanical shutter controlmode, since it is possible to eliminate the influence of smear caused byan excessive amount of incident light due to a long exposure by readingout and drain a smear component leaking to the vertical transfer CCD.Thus, a signal of high S/N (Signal-to-Noise) free from the influence ofsmear can be read out.

FIG. 6 is a view showing the shutter speed control regions of theelectronic and mechanical shutter control modes in the electronic cameraaccording to the embodiment. In FIG. 6, the electronic shutter controlmode is set to perform shutter speed control at a speed higher than 1/30sec. The mechanical shutter control mode is set to perform shutter speedcontrol at a speed lower than 1/500 sec. At a shutter speed of 1/500 secto 1/30 sec, a control mode can be selected from the electronic andmechanical shutter control modes.

The electronic camera according to the embodiment switches the controlsequence between the electronic and mechanical shutter control modes incorrespondence with a shutter speed set by the CPU 38.

The operation of the electronic camera according to the embodiment withthe above-described arrangement will be described with reference to theflow charts of FIGS. 7 and 8.

In FIG. 7, if a power switch (not shown) is turned on in step S701, theelectronic camera changes to a photographing standby state. If a switchSW1 (not shown) is turned on by, e.g., a half stroke of a release button(not shown) in step S702, the photometry device 11 executes photometryin step S703, and the focus detection device 13 performs distancemeasurement in step S704. In step S705, the photographing lens 2 isdriven based on the distance measurement result of the focus detectiondevice 13.

Based on a photographing exposure mode selected by a photographing modeselection switch (not shown), an f-number (Av value) and image sensingtime (Tv value) corresponding to the photographing exposure mode aredetermined (steps S706 to S713).

In step S706, whether the photographing exposure mode is an aperture(Av) priority mode is checked. If YES in step S706, the Av value is setto an arbitrary value chosen by the user. In step S710, a Tv value isdetermined in accordance with the photometry value measured in stepS703. Then, the flow advances to step S714.

If NO in step S706, whether the photographing exposure mode is aphotographing time (Tv) priority mode is checked in step S707. If YES instep S707, the Tv value is set to an arbitrary value chosen by the user.In step S711, an Av value is determined in accordance with thephotometry value measured in step S703. After that, the flow advances tostep S714.

If NO in step S707, whether the photographing exposure mode is a programmode is checked in step S708. If YES in step S708, Av and Tv values aredetermined in step S712 from a preset program chart (not shown) inaccordance with the photometry value measured in step S703. Then, theflow shifts to step S714.

The program chart includes various patterns. Regardless of one or aplurality of patterns, the program chart basically passes through thesame flow.

If NO in step S708, the flow shifts to step S709 to determine thephotographing exposure mode as a manual mode. Tv and Av values are setto arbitrary values chosen by the user on the basis of the photometryvalue measured in step S703. The flow advances to step S714.

In this fashion, the Tv value (target image sensing time) and the Avvalue (target f-number) are determined till step S714 regardless of aselected mode.

In step S714, whether a switch SW2 (not shown) is turned on by, e.g., afull stroke of the release switch (not shown) is checked. If NO in stepS714, whether the switch SW1 is turned off is checked in step S740. IfNO in step S740, the flow returns to step S714; or if YES, to step S702.

If YES in step S714, the CPU 38 checks in step S715 whether the Tv valuedetermined in steps S707, S710, S712, and S713 is higher than 1/30 sec(Tv< 1/30). If YES in step S715, the flow shifts to step S716 to set theexposure control mode of the electronic camera to the electronic shuttercontrol mode, as described above (see FIG. 6).

After the exposure control mode is set to the electronic shutter controlmode in step S716, the flow advances to step S717. The control circuit36 outputs a front blade traveling start signal to the mechanicalshutter 14 on the basis of an exposure control value from the CPU 38,thereby starting driving the front blades 14 a (front curtain release).Note, when a sequential photographing is performed, the front blades 14a start driving a period V1min before reading of charges accumulated inthe previous frame completes (see FIG. 5). The flow shifts to step S718.

A period of T1max+V1max (see FIG. 5) has passed after the front blades14 a starts driving, the control circuit 36 operates the solid-stateimage sensing element 15 to start a charge accumulation operation instep S718. The control circuit 36 controls the charge accumulation timeby the determined Tv value on the basis of the exposure control valuefrom the CPU 38. The flow shifts to step S719.

T2min (see FIG. 5) before the end timing of charge accumulation, thecontrol circuit 36 outputs a rear blade traveling start signal to themechanical shutter 14 in step S719. The control circuit 36 startsdriving the rear blades 14 b, and changes the solid-state image sensingelement 15 to a light-shielding state (rear curtain shielding). The flowadvances to step S726 of FIG. 8.

If NO in step S715, the flow advances to step S720 to set the exposurecontrol mode of the electronic camera to the mechanical shutter controlmode so as to control exposure by the mechanical shutter 14, asdescribed above (see FIG. 5).

In step S720, the exposure control mode is set to the mechanical shuttercontrol mode. As described above (see FIG. 3), the control circuit 36operates the solid-state image sensing element 15 in step S721 on thebasis of an exposure control value from the CPU 38, thereby starting acharge accumulation operation. In step S722, the control circuit 36outputs a front blade traveling start signal to the mechanical shutter14, thereby starting driving the front blades 14 a (front curtainrelease). Then, the control circuit 36 performs exposure to thesolid-state image sensing element 15 in step S723.

In step S724, the control circuit 36 outputs a rear blade travelingstart signal to the mechanical shutter 14 by the determined Tv value onthe basis of the exposure control value from the CPU 38. The controlcircuit 36 starts driving the rear blades 14 b to shield an objectimage, and ends the exposure operation to the solid-state image sensingelement 15 by the front and rear blades 14 a and 14 b (rear curtainshielding).

After traveling of the rear blades of the mechanical shutter 14 ends,the solid-state image sensing element 15 continues the chargeaccumulation operation. To eliminate the influence of smear caused by anexcessive quantity of incident light in exposure, the solid-state imagesensing element 15 reads out (vertically transfers) and drains a smearcomponent leaking to the vertical transfer CCD before shifting signalcharges accumulated in the photoelectric conversion elements of thesolid-state image sensing element 15 to the vertical transfer CCD.Thereafter, the flow advances to step S726 of FIG. 8.

In FIG. 8, the solid-state image sensing element 15 ends the chargeaccumulation operation in step S726, and transfers signal chargesaccumulated in the photoelectric conversion elements to the verticaltransfer CCD. Note, when the electric shutter control mode has beenselected, this transfer operation starts a period T2max+V2max after therear blades 14 b start driving (see FIG. 5). Further, the solid-stateimage sensing element 15 executes a normal reading operation which is asignal charge reading operation. Image processing is done in step S727,an image is recorded on the memory card 34 in step S728, and thisprocessing operation ends in step S730.

At the same time as image processing in step S727, whether the switchSW1 (not shown) is turned on by a half stroke of the release button (notshown) is checked in step S729. If NO in step S729, the processingoperation ends in step S730; whereas if YES, the CPU 38 determines thatthe photographing mode is a sequential shooting mode. The flow shifts tostep S731 for preparations for the photography of the next frame.Photometry by the photometry device 11, and determination of Tv and Avvalues by the same operation as that in steps S706 to S713 areperformed.

Whether the switch SW2 (not shown) is turned on by a full stroke of therelease button (not shown) is checked in step S732. If NO in step S732,sequential shooting is determined to have been suspended. The electroniccamera shifts to the standby state in step S733, and whether the switchSW1 is turned off is checked in step S741. If NO in step S741, theelectronic camera waits in the standby state, and the flow returns tostep S732, and if YES in step S741, the sequential shooting isterminated. If YES in step S732, the flow advances to step S734 in orderto perform a photographing operation of the next frame.

In step S734, the shutter control mode of the preceding frame ischecked, i.e., whether the previous mode is the electronic shuttercontrol mode is checked.

If YES in step S734, the CPU 38 determines in step S736 whether thecurrent Tv value is higher than 1/30 sec (Tv< 1/30). If YES in stepS736, the CPU 38 sets the electronic shutter control mode in step S738,and

performs an exposure operation of the next frame in step S739 by thesame operation as that in steps S717 to S719. If the current Tv value isdetermined to be equal to or lower than 1/30 sec (Tv≧ 1/30) in step S736(NO), the CPU 38 sets the mechanical shutter control mode in step S737,and performs an exposure operation of the next frame in step S739 by thesame operation as that in steps S721 to S725.

If photography of the previous frame is determined in step S734 to benot the electronic shutter control mode but the mechanical shuttercontrol mode, the flow advances to step S735, and the CPU 38 checkswhether the current Tv value is lower than 1/500 sec (Tv> 1/500). If YESin step S735, the flow advances to step S737. The CPU 38 sets themechanical shutter control mode, and performs an exposure operation ofthe next frame in step S739 by the same operation as that in steps S721to S725.

If the current Tv value is determined in step S735 to be higher than1/500 sec (Tv< 1/500), the flow shifts to step S738. The CPU 38 sets theelectronic shutter control mode, and performs an exposure operation ofthe next frame in step S739 by the same operation as that in steps S717to S719.

In the electronic camera according to the embodiment, the overlap regionbetween the control ranges of the electronic and mechanical shuttercontrol modes is set as a hysteresis region. Even if the exposurecontrol value changes, the exposure control sequence preferentiallycontinues in photography of a preceding frame. This prevents frequentswitching of the exposure control sequence at the boundary of a givenshutter speed every time exposure of an object to be photographedchanges during sequential shooting.

As described above, this embodiment greatly increases the exposure speed(shutter speed) without using a high-performance mechanical shutter, andsets the low-speed range to the mechanical shutter control mode.Degradation of an image caused by smear of an image sensing element canbe prevented at low cost.

An overlap region is set in switching between the electronic andmechanical shutter control sequences. This can prevent switching of thesequence upon taking every picture, and can realize smooth switching ofthe sequence.

A hysteresis region is set in switching between the electronic andmechanical shutter control sequences. This can prevent switching of thesequence at a given shutter speed upon taking every picture, can realizesmooth switching of the sequence, and can prevent the user from feelingincompatibility in switching the sequence.

When exposure is controlled by both the mechanical and electronicshutters, the mechanical shutter is driven by a time which considersindividual variations in advance with respect to individual variationsin exposure control time caused by the mechanical delay of themechanical shutter. Variations in exposure time caused by the mechanicaldelay of the mechanical shutter need not be measured/adjusted, smoothlysimplifying the assembly and reducing the cost.

Since the driving start timing of the mechanical shutter overlapsdriving of the image sensing element (traveling of the front/rear bladesof the mechanical shutter starts during driving of the image sensingelement), a stable frame speed in sequential shooting and an increase inspeed can be achieved.

Other Embodiment

The present invention can be applied to a system 20 constituted by aplurality of devices (e.g., host computer, interface, camera head) or toan apparatus comprising a single device (e.g., digital camera).

Further, the object of the present invention can also be achieved byproviding a storage medium storing 25 program codes for performing theaforesaid processes to a computer system or apparatus (e.g., a personalcomputer), reading the program codes, by a CPU or MPU of the computersystem or apparatus, from the storage medium, then executing theprogram.

In this case, the program codes read from the storage medium realize thefunctions according to the 5 embodiment, and the storage medium storingthe program codes constitutes the invention.

Further, the storage medium, such as a floppy disk, a hard disk, anoptical disk, a magneto-optical disk, CD-ROM, CD-R, a magnetic tape, anon-volatile type memory card, and ROM can be used for providing theprogram codes.

Furthermore, besides aforesaid functions according to the aboveembodiment are realized by executing the program codes which are read bya computer, the present invention includes a case where an OS (operatingsystem) or the like working on the computer performs a part or entireprocesses in accordance with designations of the program codes andrealizes functions according to the above embodiment.

Furthermore, the present invention also includes a case where, after theprogram codes read from the storage medium are written in a functionexpansion card which is inserted into the computer or in a memoryprovided in a function expansion unit which is connected to thecomputer, CPU or the like contained in the function expansion card orunit performs a part or entire process in accordance with designationsof the program codes and realizes functions of the above embodiment.

In a case where the present invention is applied to the aforesaidstorage medium, the storage medium stores program codes corresponding tothe timing charts shown in FIGS. 3 to 5 and the flowcharts shown inFIGS. 7 and 8 described in the embodiment.

The present invention is not limited to the above embodiments andvarious changes and modifications can be made within the spirit andscope of the present invention. Therefore to apprise the public of thescope of the present invention, the following claims are made.

1. An image sensing method of sensing an image by an image sensingapparatus having an electronic shutter for controlling a chargeaccumulation time of an image sensing element and a mechanical shutterfor releasing/shielding an optical path to the image sensing element,the method having a first control mode of controlling an image sensingperiod mainly by the electronic shutter, comprising: a control step ofcontrolling operations of the electronic and mechanical shutters so asto overlap each other, and a charge reading period of the image sensingelement and part of a release operation period of the mechanical shutterare controlled to overlap each other.
 2. The method according to claim1, wherein in said control step, the charge accumulation period of theimage sensing element and part of a shielding operation of themechanical shutter after release of the mechanical shutter arecontrolled to overlap each other.
 3. The method according to claim 2,wherein the mechanical shutter has front blades for releasing theoptical path to the image sensing element and rear blades for shieldingthe optical path to the image sensing element, and letting T2min be ashortest time until shielding of a predetermined region starts after therear blades start a shielding operation, the shielding operation of therear blades starts T2min before end time of charge accumulation in theimage sensing element in said control step in the first control mode. 4.The method according to claim 1, further comprising: a second controlmode of controlling a photographing time mainly by the mechanicalshutter; and a switching step of switching between the first and secondcontrol modes.
 5. The method according to claim 4, wherein in saidswitching step, the first and second control modes are switched inaccordance with the photographing time.
 6. The method according to claim5, wherein in said switching step, the first and second control modesare switched in accordance with the photographing time and either one ofthe first and second control modes used in previous photography.
 7. Themethod according to claim 4, wherein in said switching step, (a) a firstphotographing mode is set when previous photography is performed in thefirst photographing mode and a current photographing time is shorterthan a first photographing time, (b) a second photographing mode is setwhen previous photography is performed in the first photographing modeand the current photographing time is longer than the firstphotographing time, (c) the first photographing mode is set whenprevious photography is performed in the second photographing mode and aphotographing time used in current photography is shorter than a secondphotographing time which is shorter than the first photographing time,and (d) the second photographing mode is set when previous photographingis performed in the second photographing mode and the photographing timeused in current photography is longer than the second photographingtime.
 8. The method according to claim 4, wherein unwanted charges intransfer means for transferring charges of the image sensing element aredrained prior to transfer of charges of the image sensing element in thesecond control mode.
 9. The method according to claim 1, wherein theimage sensing element includes a charge-coupled device.
 10. The methodaccording to claim 1, wherein the image sensing apparatus includes anelectronic camera.
 11. An image sensing method of sensing an image by animage sensing apparatus having an electronic shutter for controlling acharge accumulation time of an image sensing element and a mechanicalshutter for releasing/shielding an optical path to the image sensingelement, the method having a control mode of controlling an imagesensing time mainly by the mechanical shutter, comprising: a controlstep of draining unwanted charges of transfer means prior to transfer ofcharges of the image sensing element in the control mode.
 12. The methodaccording to claim 11, wherein the image sensing element includes acharge-coupled device.
 13. The method according to claim 11, wherein theimage sensing apparatus includes an electronic camera.
 14. An imagesensing apparatus having an electronic shutter for controlling a chargeaccumulation time of an image sensing element and a mechanical shutterfor releasing/shielding an optical path to the image sensing element,and having a first control mode of controlling an image sensing timemainly by the electronic shutter, comprising: a controller adapted tocontrol operations of the electronic and mechanical shutters so as tooverlap each other, and controlling a charge reading period of the imagesensing element and part of a release operation period of the mechanicalshutter to overlap each other.
 15. The apparatus according to claim 14,wherein said controller controls the charge accumulation period of theimage sensing element and part of a shielding operation of themechanical shutter after release of the mechanical shutter so as tooverlap each other.
 16. The apparatus according to claim 15, wherein themechanical shutter has front blades for releasing the optical path tothe image sensing element and rear blades for shielding the optical pathto the image sensing element, and letting T2min be a shortest time untilshielding of a predetermined region starts after the rear blades start ashielding operation, said controller controls to start the shieldingoperation of the rear blades T2min before end time of chargeaccumulation in the image sensing element in the first control mode. 17.The apparatus according to claim 14, further comprising: a secondcontrol mode of controlling a photographing time mainly by themechanical shutter; and a switch adapted to switch between the first andsecond control modes.
 18. The apparatus according to claim 17, whereinsaid switch switches between the first and second control modes inaccordance with the photographing time.
 19. The apparatus according toclaim 18, wherein said switch switches between the first and secondcontrol modes in accordance with the photographing time and either oneof the first and second control modes used in previous photography. 20.The apparatus according to claim 17, wherein said switch (a) sets afirst photographing mode when previous photography is performed in thefirst photographing mode and a current photographing time is shorterthan a first photographing time, (b) sets a second photographing modewhen previous photography is performed in the first photographing modeand the current photographing time is longer than the firstphotographing time, (c) sets the first photographing mode when previousphotography is performed in the second photographing mode and aphotographing time used in current photography is shorter than a secondphotographing time which is shorter than the first photographing time,and (d) sets the second photographing mode when previous photographingis performed in the second photographing mode and the photographing timeused in current photography is longer than the second photographingtime.
 21. The apparatus according to claim 17, wherein said controllercontrols to drain unwanted charges in transfer means for transferringcharges of the image sensing element, prior to transfer of charges ofthe image sensing element in the second control mode.
 22. The apparatusaccording to claim 14, wherein the image sensing element includes acharge-coupled device.
 23. The apparatus according to claim 14, whereinthe image sensing apparatus includes an 15 electronic camera.
 24. Animage sensing apparatus having an electronic shutter for controlling acharge accumulation time of an image sensing element and a mechanicalshutter for releasing/shielding an incident optical path to the imagesensing element, and having a control mode of controlling an imagesensing time mainly by the mechanical shutter, comprising: a controlleradapted to drain unwanted charges of transfer means for transferringcharges of the image sensing element, prior to transfer of charges ofthe image sensing element in the control mode.
 25. The apparatusaccording to claim 24, wherein the image sensing element includes acharge-coupled device.
 26. The apparatus according to claim 24, whereinthe image sensing apparatus includes an 5 electronic camera.
 27. Animage sensing apparatus comprising: an image sensing element; amechanical shutter adapted to release and shield an optical path to saidimage sensing element; and a control device adapted to controlstart/stop of charge accumulation of said image sensing-element andreleasing/shielding operation of said mechanical shutter so that theshielding operation of said mechanical shutter is started before chargeaccumulation of said image sensing element is stopped.
 28. A computerprogram product comprising a computer usable medium having computerreadable program code means embodied in said medium for sensing an imageby an image sensing apparatus having an electronic shutter forcontrolling a charge accumulation time of an image sensing element and amechanical shutter for releasing/shielding an optical path to the imagesensing element, the method having a first control mode of controllingan image sensing period mainly by the electronic shutter, said productincluding: computer readable program code means for controllingoperations of the electronic and mechanical shutters so as to overlapeach other, and a charge reading period of the image sensing element andpart of a release operation period of the mechanical shutter arecontrolled to overlap each other.
 29. A computer program productcomprising a computer usable medium having computer readable programcode means embodied in said medium for sensing an image by an imagesensing apparatus having an electronic shutter for controlling a chargeaccumulation time of an image sensing element and a mechanical shutterfor releasing/shielding an optical path to the image sensing element,the method having a control mode of controlling an image sensing timemainly by the mechanical shutter, said product including: computerreadable program code means for draining unwanted charges of transfermeans prior to transfer of charges of the image sensing element in thecontrol mode.